1. Field of the Invention
This invention relates generally to a hollow-fibre permeability apparatus, and more particularly to hollow fibre permeability apparatus in which a permeating region of a housing contains a bundle of hollow fibres, and materials can selectively permeate through the membranes formed by the permeable walls of the hollow fibres, between a fluid flowing in the open spaces of the bundle of hollow fibres, and another fluid flowing inside the hollow fibres. The permeation may be based on the principles of osmosis, dialysis, ultrafiltration, reverse osmosis or the like.
2. Description of the Prior Art
For example, a conventional hollow-fibre permeability apparatus is used for blood dialysis in an artificial kidney, in which toxic materials are removed from the blood of a patient suffering from renal failure or medicinal poisoning.
The hollow fibres used in the blood dialysis apparatus provide a relatively large effective surface area of membrane. Therefore, the apparatus can be smaller than conventional coil-type or plate-type blood dialysis apparatus. Thus, the blood priming volume can be smaller, which is beneficial to the patient during dialysis. The apparatus is also easier to handle, and the hollow fibres are superior in withstanding pressure and for ultrafiltration.
Since the blood dialysis apparatus has many advantages above described, it has become popular recently. However, the apparatus has the following disadvantages.
Since the ten to fifteen thousand hollow fibres are closely bundled in the cylindrical housing, it is difficult for the dialysate to pass uniformly through the whole of the bundle. It is experimentally proved that the dialysate flow rate is higher around the peripheral region of the bundle adjacent to the inner surface of the housing, and the dialysis is extremely low in the central region of the bundle. It is also found that boundary layers are formed along the outer surfaces of the hollow fibres which reduce the dialysis efficiency.
In order to remove the above described disadvantages, a novel hollow-fibre permeability apparatus was already proposed in the U.S. Application No. 653,351 now U.S. Pat. No. 4,082,670, by the same applicant in which at least one portion of the housing is of enlarged cross-section relative to the bundle to define a space between the bundle and a wall of the housing into which at least part of the first fluid can pass in its passage from the inlet to the outlet tube, and the shape of the enlarged cross-section portion promotes cross-flow of the first fluid relative to the fibers.
As the results of further studies, this inventor has found out that the shape of the inlet and outlet portions, and more particularly of the inlet portion for the dialysate greatly affect the flow of the dialysate in the housing, and that the improvement of the shape is very important.
The inlet and outlet portions for dialysate are until now circular in cross section, and so are locallized in a much limited position to the permeating region of the housing. Accordingly, the dialysate does not flow uniformly through the whole bundle. This is quite unfavourable in view of the dialysis efficiency, because the contact of the dialysate with membrane is not ideal. The dialysate flow in the housing can be visualized by introducing black ink in the dialysate.